1. Field of the Invention
This invention relates to logic units for pulsed circuits and more particularly to such logic units having saturable magnetic cores which pass applied pulse signals in the presence of a d-c control current and block the applied pulse signals in the absence of the control current.
2. Background Information
Dynamic logic units are logic circuits which operate with pulsed signals. One type of logic unit for pulse circuits is disclosed in U.S. Pat. No. 4,661,310. This logic unit includes a core of rectangular hysteresis loop material on which is wound an input winding, a control winding and an output winding. A d-c current of sufficient magnitude to saturate the core in one direction is selectively applied to the control winding. The pulse signal applied to the input winding is of a polarity and magnitude sufficient to drive the core into saturation in the opposite direction. Thus, with the control winding energized, the core experiences large flux reversals as it is alternately driven into saturation in one direction and then the other. This generates a pulse signal on the output winding. With the control winding deenergized the pulses are essentially blocked as the core remains saturated in the direction imposed by the input pulses.
In order to generate a true representation of the input pulses from the pulses appearing on the output winding, which are induced by the leading and trailing edges of the input pulses, a flip-flop is connected to the output winding. In addition, low pass R-C filters are connected between the output winding and the set and reset inputs of the flip-flop to prevent voltage spikes generated on the output winding when the control winding is deenergized from switching the flip-flop.
It has been found that these low pass R-C filters, although effective, integrate the signal on the output winding and deteriorate the leading edge of this signal which is input to a CMOS flip-flop. This, in turn, causes variations in the duty cycle of the waveform at the flip-flop output. In addition, where these dynamic logic units are used in protection systems for nuclear power plants, they must meet the Nuclear Regulatory Commission requirement that any single failure will not produce an undesired condition. There is some concern that a common mode failure of both filter capacitors would allow the flip-flop to continue to toggle on the unfiltered spikes.
In view of the above, there is a need for dynamic logic units utilizing saturable magnetic cores with improved response times; and
There is also a need to provide such logic units which are economical to produce and require a minimum amount of circuit real estate.